This invention relates to a chemical sensor ("optrode") for the quantitative measurement of selected volatile organic and inorganic molecules in atmospheres. This is a refinement of the optrode design of Milanovich et al. The optrode has been modified in several important ways to allow for ease of manufacture and greater sensitivity.
The simplified design and operation of the optrode coupled with chemical specificity and low limits of detection makes the invention an attractive alternative to other forms of chemical analysis. The optrode has been shown to attain the precision and accuracy of gas chromatography with photoionization or Hall detectors for selected organic molecules, such as trichloroethene and chloroform. However, the optrode attains this performance without the need for preconcentration (such as purge and trap) or Hall detectors for selected organic molecules, such as thichloroethene and chloroform. However, the optrode attains this performance without the need for preconcentration (such as purge and trap) or separation (chromatography) steps. The optrode has been found to have a limit of detection of 1 part per billion of trichloroethene in water with 1,2-dichloroethene and tetrachloroethene present. Because of these performance factors and the ease of use of the optrode, there are many applications in environmental, health & safety, medical and process control fields for such a chemical sensor.
One of the important applications of the optrode is the creation of "real-time" sampling/analytical units for the monitoring of trichloroethene in ground water. The cost savings to the government and industry in avoiding the cost of manually sampling the sells, disposal of the purge water and the cost of the analytical laboratory over the lifetime of a ground-water restoration project can be significant.
Current optrode technology is divided into two primary types of designs. The most prevalent type of design in the literature is fabricating the optrode body from some type of inert material, and providing a port or area in the wall to be fitted with a permeable material. The species of interest, i.e. trichloroethene, passes through the permeable membrane and reacts with the reagent contained within the body of the sensor. Examples of the first type of optrode are Klainer et al., U.S. Pat. No. 5,116,759, and Miller et al., U.S. Pat. No. 4,666,674. The second type of optrode uses a permeable tube which serves as the body of the optrode. This type of sensor was developed by Milanovich it al. at Lawrence-Livermore National Laboratory, Livermore, Calif. The original design was disclosed in a series of papers. The design was very difficult to manufacture and suffered from several material compatibility problems. The reagents used in the design attacked the seals and other components reducing the life of the optrode.
This invention relates to a simplified design of the optrode which increases the life of the device while providing lower noise and resolution of other associated problems.